A variety of food products are packaged and sold in cans of the type having a cylindrical can body and a pair of end closures applied to the ends of the can body for sealing the contents in the can. The can body is typically formed of metal, paper, and/or plastic materials, and the end closures may be made of materials that are similar or dissimilar to that of the can body.
It is clearly desirable for a can to retain the integrity of its structure and seals during handling and storage of the can prior to the can being opened by the consumer. Where elevated pressures exist in the can, it is desirable that the can body not burst and the end closures remain attached and sealed on the ends of the can body until the consumer opens the can. Additionally, in some types of cans, the end closures are applied to the can body in a manner so as to intentionally permit air in the can to be vented through the end seals when the air exceeds outside pressure by a certain amount. Unless this excess pressure is properly vented, pressure in the can may build to a high enough level to cause the body to burst or an end closure to be blown off the can.
Accordingly, it is evident that it is desirable for can manufacturers and packagers to be able to control can strength and leakage characteristics. One way of facilitating such control is by testing can samples to determine such characteristics so that manufacturing or design defects may be discovered and corrected. Thorough testing requires determination of can body strength characteristics, as well as leakage and strength characteristics of a can body and end closure combination.
A can vent testing device is known from U.S. Pat. No. 5,596,137 issued to Perry et al. The device includes a mechanism for sealing against an inner surface of a can adjacent its open end to create a sealed chamber in the can bounded on the other end by the end closure. A disadvantage of the device and method of the Perry patent is that the testing apparatus and method are limited to determining leakage rate for a composite can having an end closure crimp sealed onto the end of a can body. The apparatus and method are not capable of determining strength characteristics of a can body alone, or of determining strength of a can body and end closure combination through a closure blow-off test or the like.
Another disadvantage of the device of Perry is that the sealing mechanism does not include any means for preventing the can from being blown off the sealing mechanism by air pressure in the can during testing, and therefore Perry provides a positioning bar which abuts the end closure to retain the can on the sealing mechanism. However, pressure exerted on the end closure by the positioning bar has the potential to significantly affect leakage rate through the crimp seal of a composite can, making the test results non-representative of the leakage rate of an unrestrained can.